The present invention relates to a conveyor system for a sheet of printing material in a printing material processing machine, including a running member which can be moved through the machine along a transport path using a drive, and further including a number of encoders which are arranged along the transport path and used to sense the position of the running member. Moreover, the present invention relates to a method for generating a drive signal of a conveyor system, including a running member, for a sheet of printing material in a printing material processing machine, by evaluating signals of a number of encoders which are distributed along a transport path of the running member.
In printing material processing machines, such as printing units, printing presses, print finishing machines (folding apparatuses, gatherer-stitchers, adhesive binders, or similar), or the like, the movement of a sheet of printing material, typically on a section of a transport path of conveying elements, can be accomplished using a conveyor system controlled in open or closed loop. The conveying elements include holding means or fixing means for holding a sheet of printing material at least during an interval of time. When moving elements, so-called xe2x80x9crunning membersxe2x80x9d on a long, in particular, closed transport path in a circuit, it is first of all required to use a suitable drive, such as a flexible drive, a rack-and-pinion drive, a linear motor, or the like; secondly, it is required to feed back the positional information to the controller for closed-loop operation.
In the case that a linear motor is used, energy supply to the conveyor system is typically provided by synchronous motors of which the secondary member is moved, that is, forms the running member. It is also possible to use a plurality of secondary members or running members. The static member includes the primary member, which is suitably segmented to be able to drive a plurality of running members on one path. In order to sense the position of the running member, that is, for signal acquisition purposes, diverse configurations of suitable encoder arrangements for generating a signal by detection and suitable detection objects have already been proposed.
To acquire the positional information of the conveyor system, different principles are available whose scale members and encoders (i.e., also sensors) can be designed and arranged differently. In the prior art, there are length measuring systems which are based on optical, magnetostrictive, electrostatic, or inductive and/or resistance principles. In principle, the measuring systems differ from each other in their measurement method, which can either be an implicitly absolute or an incremental one. A common shortcoming of known measuring systems is the limited length of their measuring path for high-accuracy position sensing at high speed. In other words, it turns out to be very difficult to achieve high position resolution at high speeds over a long section of the transport path for a running member in a transport system.
A conveyor system for conveying material in sheet form or sheets of printing material in a rotary printing press is disclosed, for example, in German Patent Application No. 197 22 376 A1. This conveyor system includes two guide rails running parallel to each other, in each of which one associated propulsion element is guided in a play-free manner, the propulsion element forming the running member of an electric linear drive. For example, according to German Patent Application No. 197 22 376 A1, the two propulsion elements are designed as link chains having at least two individual links of magnetizable material and connected by a cross-member to which are mounted grippers for holding the sheet. The propulsion elements are driven by drive stations that are located outside the guide rails and have coils which form the stator of the linear drive and which are spaced apart at distances substantially smaller than or equal to the length of the propulsion devices.
German Patent Application No. DE 101 62 448 A1 describes a device for sensing the position of a running member in a conveyor system of a printing material processing machine. A number of encoders which, in particular, can be evenly spaced apart from each other, are arranged along a position coordinate line of a (preferably closed) transport path. The conveyor system drive is preferably a linear motor; the running member has a scale member or a position mark. The scale member or the position mark can be linear in shape or punctiform. Preferred embodiments of the measuring system are optical encoders or magnetic field detectors. The encoders are arranged such that at certain positions of the running member, at least two neighboring encoders deliver non-vanishing signals. This arrangement can also be referred to as overlapping arrangement.
An object of the present invention is to provide a conveyor system for a sheet of printing material in a printing material processing machine such that the driving of the conveyor system is guaranteed with high quality.
According to the present invention, a conveyor system for a sheet of printing material in a printing material processing machine includes a running member which can be moved through the printing material processing machine along a transport path using a drive (drive control and driving element), as well as a number of encoders which are arranged along the transport path, preferably in an overlapping arrangement, and used to sense the position of the running member. The printing material is capable of being held on the running member at least along a section of the transport path or path of the running member. The encoders are connected to an evaluation unit for progressive sampling of the encoder signals. In the evaluation unit, an active encoder and a passive encoder can be specified at least for an interval of time so that in a signal processor unit of the evaluation unit a drive signal, in particular, an incremental signal, can be or is generated on the basis of a change in amplitude of the signal of the active encoder and a change in amplitude of the signal of the passive encoder. For different time intervals, the active and passive encoders can be different. The transport path of the running member is preferably closed. In said time interval, the change in amplitude of the active encoder can be used during a first period of time and the change in amplitude of the passive encoder can be used during a second period of time for generating the drive signal. Preferred encoders are so-called xe2x80x9csine/cosine encodersxe2x80x9d, that is, encoders having two encoders signals which are shifted in phase relative to each other.
According to the present invention, a method for generating a drive signal of a conveyor system, including a running member, for a sheet of printing material in a printing material processing machine is based on the evaluation of signals of a number of encoders which are distributed along a transport path the running member and which, in particular, can be evenly spaced apart from each other: The encoders are sampled progressively. Out of the number of encoders, an active encoder and a passive encoder are specified at least for an interval of time. A drive signal is generated on the basis of a change in amplitude of the signal of the active encoder and a change in amplitude of the signal of the passive encoder.
In different time intervals, it is possible to specify different active and passive encoders of the number of encoders. In particular, a so-called xe2x80x9chandoverxe2x80x9d from a first active and a first passive encoder in a first time interval to a second active and a second passive encoder in a second time interval can take place. These handovers can be continued between further time intervals in a corresponding manner for further encoders. The generation of a drive signal is based on the change in amplitude of a signal of one of the number of encoders that has been determined to be the active encoder for a time interval; the active encoder or the passive encoder being monitored such that a decision can be made whether to specify a different active encoder and a different passive encoder for a different time interval.
In the conveyor system and the method according to the present invention, the evaluation of the encoder signals makes available, on one hand, the velocity information (change of position of the running member) and, on the other hand, the phase information (precise position of the running member) of the encoders distributed along the transport path: The drive signal can be generated starting from an initial value (initial amplitude and initial phase), because the required change in the drive signal for driving the conveyor system is derived from the position and the change in position of the running member and can therefore be determined. Using the change in amplitude, at a current point in time, of the encoder signal of the encoder that has been determined to be the active encoder for the current time interval, it is possible to determine the change in the drive signal with the instantaneous amplitude and the instantaneous phase at this point of time. From the examination of the change in amplitude of the signal of the active encoder and also of the change in amplitude of the signal of the passive encoder, or from the determination of the number of zeros of the signal of the passive encoder, it becomes clear whether, at the current moment, the running member has moved away from the active encoder of the number of encoders and approached another encoder, in particular the passive encoder, to such an extent that a changeover, i.e., determination of a new active encoder and a new passive encoder of the number of encoders must take place. As a consequence, in order for the distance of the old active encoder to the new active encoder to be taken into account at the input side to calculate the drive signal, a phase shift and a change in amplitude are required as a function of the above-mentioned distance compared to the motor period (i.e., the path traveled by the running member during a motor cycle). On the output side, the drive signal (instantaneous amplitude and instantaneous phase) is not changed by the encoder changeover. In other words, in the conveyor system and the method according to the present invention, the evaluation of the encoder signals uses the change in an encoder signal of a currently active encoder to generate a drive signal; different encoders being currently active encoders for different time intervals, taking into account the distances of the encoders relative to each other.
The evaluation according to the present invention is, in principle, independent of the number of encoders. A control signal is generated from a plurality of encoder signals with precision and taking into account the instantaneous velocity of the running member. The evaluation unit can be advantageously scaled according to the number of encoders. A downstream drive is relieved from the processing of a number of encoder signals, because a drive signal is generated in the evaluation unit. In other words, the incremental changeover is relocated; only a generated incremental signal is transferred. Furthermore, a changeover from a first active encoder to a second active encoder is easily accomplished based on the determination of the number of zeros of the signal of the passive encoder by counting. This minimal information is sufficient to allow an assessment as to whether the position of the running member in the conveyor system can still be determined with sufficient accuracy using the signal of the first active encoder.
The evaluation unit of the conveyor system according to the present invention can include at least one multiplexer for the encoder signals as well as a control unit. A preferred cycle time is below 250 microseconds. For the conveyor system according to the present invention, it is preferred that the drive of the conveyor system is a variable-speed drive and that the drive signal is a measure of the actual value of the position of the running member. It is clear to one skilled in the art that it is also possible to generate a plurality of drive signals for a plurality of running members. In other words, the conveyor system can include a control device, which can be linked to the machine control to exchange data and/or signals, in particular setpoint values and actual values for the position of the running member or members.
In a preferred embodiment, the drive of the inventive conveyor system for a sheet of printing material in a printing material processing machine is a linear motor. Moreover, the evaluation unit can contain at least one analog-to-digital converter, and the signal processor unit can be a digital signal processor unit. In a further refinement, the evaluation unit can contain at least one digital-to-analog converter, in which at least one output signal of the signal processor unit can be converted.
It is particularly advantageous if in the inventive conveyor system for a sheet of printing material, each two successive encoders of the number of encoders along the transport path are substantially equally spaced apart. For the drive, this means that an equal phase shift or an equal period of time occurs between the positions of two encoders in relation to the cycle of the drive. Moreover, provision can be made for at least one reference pulse generator or an absolute encoder. In this manner, an initial phase can be determined for the drive of the running member in an easy way.
A preferred encoder type is magnetic field detectors; the running member featuring a scale member having a magnetic pattern (dipole, multipole, or regular magnetization pattern, such as a stripe pattern, or the like). At this point, it should be mentioned that the topology and the mode of operation of the evaluation unit are independent of the measurement method used. However, non-optical, magnetic or inductive detection is particularly advantageous when processing printing material in an environment in which absolute cleanness is not always guaranteed.
The conveyor system according to the present invention can advantageously be used in a printing unit, in particular, in a planographic printing unit, a flexographic printing unit, or an offset printing unit. In other words, a printing unit according to the present invention features a conveyor system according to the present invention. A printing unit according to the present invention can be used, in particular, in a printing press. In this context, the printing press can have a continuous drive for moving the sheets of printing material, or a number of individual drives. In other words, a printing press according to the present invention has at least one inventive printing unit, in particular, also a feeder and a delivery. A preferred embodiment of a printing press according to the present invention includes a feeder, at least one printing unit, and a delivery. An alternative embodiment includes a feeder, at least one printing unit, and a finishing unit. The finishing unit is, for example, a varnishing unit, a dryer, a cutting device, or a print finishing machine. The preferred embodiment and the alternative embodiment are characterized by at least one conveyor system according to the present invention. The conveyor system according to the present invention can be used for moving or transporting between the feeder and a printing unit and/or between a printing unit and a further printing unit and/or between a printing unit and a delivery and/or between a printing unit and a finishing unit. Typically, a printing press according to the present invention contains four, five, eight, or ten printing units.
The method according to the present invention for generating a drive signal of a conveyor system for a sheet of printing material in a printing material processing machine can be further developed in an advantageous manner in that the initial phase of the drive signal is determined by measuring the position of the running member at a first point in time. Moreover, provision can be made to specify a different active encoder and a different passive encoder when a certain number of zeros of the signal of the passive encoder has been counted. Preferably, the other active encoder is the current passive encoder.
During changeover from a first active encoder and a first passive encoder to a second active encoder and a second passive encoder, it is possible, knowing the distance between the first and second active encoders, knowing the distance between the first and second passive encoders as well as the path traveled during a motor cycle, to infer the associated phase shift of the drive signal in a simple and accurate manner.
In the context of the inventive idea, there is also-a method for open-loop control of a drive of a conveyor system for a sheet of printing material in a printing material processing machine, a drive signal being generated by evaluating signals of a number of encoders according to the method of the present invention. The described technical teaching also discloses a method for closed-loop control of a drive of a conveyor system for a sheet of printing material in a printing material processing machine, a drive signal being generated as a measure of the actual value of the position of the running member by evaluating signals of a number of encoders according to the method of the present invention.